Photoelectric colorimeter



Mar qh 21, 1950 e. c. ELTENTON ETAL 2,501,599

PHOTOEQILECTRIC COLORIMETER Filed Nov. 8, 1947 3 Sheets-Sheet 5 \nvzniors: Georgc C. EHzMon Marvin E). Fallqm rzr 5g their AH'orncq:

' Patented Mar. 21, 1959 UNITED STATES PATENT OFFICE PHOTOELECTRIC COLORIMETER George (J. Eltenton, Berkeley, and Marvin B. Fallgatter, San Leandro, Calif., assignors to Shell Development Company, San Francisco,

Calif., a corporation of Delaware Application November 8, 1947, Serial No. 784,924

4 Claims. 1

This invention relates to an apparatus and a method for measuring the relative color densities of fluids and pertains more particularly to a photoelectric colorimeter for determining and recording the relative color density or optical transmissivity of continuously flowing fluids. The use of photoelectric analytical apparatus for process control in plant production or manufacturing has been so far limited, as little advance has been made in the development of instruments of simple and sturdy design adapted to be used in continuous flow processes.

Photoelectric instruments to be used for continuous operation must necessarily contain means of compensating for the inherent errors in such tion of the photocell sensitivity, contamination,

by dust, etc., of the light source, collimating slits or photocell surfaces, or contamination of the inner surfaces of the inspection or test chamber by the continuously flowing fluid to be tested. In photoelectric instruments incorporating two or more photocells, there may be differential deterioration of the photocell sensitivities as well as differential contamination of the lamps, collimating slits and photocell surfaces.

Photoelectric colorimeters designed and used for colorimetric determinations in the laboratory have been based on the principle of comparing the color of an unknown fluid against the color of a known standard colored solution, filter or glass disc, etc. Generally, colorimetric apparatuses of this type have notbeen entirely satisfactory, as only individual samples could be tested. The test procedure was therefore time consuming, the apparatus had to be cleaned after each test, and it was usually difiicult or impossible to test a continuously flowing fluid.

It is therefore an object of the present invention to provide an apparatus, incorporating photoelectric means, for detecting, measuring and recording changes in color density of a continuously flowing fluid stream.

It is also an object of the invention to provide a photoelectric colorimeter having means for compensating for variations in the line voltage of the light source.

It is a further object of the present invention to provide a photoelectric colorimeter incorporating means for detecting and compensating for a 2 decrease in photocell sensitivity or for contamination of the light source, collimating slit or photocell surface. I

A further object of the present invention is to provide a photoelectric colorimeter for analyzing a continuously flowing fluid which exerts a cleaning action on the test chamber of the colorimeter, said colorimeter having means adapted to detect any differential deterioration of the glass surfaces of the test chamber.

It is a still further object of this invention to provide a photoelectric colorimeter for determining the color density of a continuously flowing fluid while incorporating into said colori- 7 meter a standard colored-solution, disc or filter.

Other objects and advantages of the invention will become apparent from the following detailed description taken with reference to the drawings wherein:

Figure 1 is a view, partially in cross section, of a preferred embodiment of the photoelectric colorimeter of the presentinvention.

Figure 2 is a cross sectional view taken along line '22 in Figure 1.

Figure 3 is an electrical diagram of a potentiometer device used in the system of the present invention.

Figures 4 and 5 are diagrammatic top views of the device of Figure 1 with the top of the housing removed and the photocells in operating positions.

Figures 6, '7, 8 and 9 are diagrammatic top views of modifications of the device illustrated in Figures 1, 2, 4 and 5 with the top of the housing removed.

Figure 10' is a diagrammatic view, partly in cross section, of another embodiment of the present invention;

Figure 11 is a diagrammatic representation of a control system embodying the present invention.

A preferred embodiment of the present photoelectric colorimeter is shown in Figures 1 and 2. It comprises essentially a base member 50, transparent cylinders II and 12, cell cover I3, housing or carriage member [4, light source l5, photocell means l8 and I9 and fluid inlet and outlet means 3'! and 38 (Figure 2) respectively.

The base member of pedestal l0 may be of any shape having upper and lower flange members 22 and 23, respectively, and an axial bore 241 passing therethrough. The lower flange member 23 may be equipped with bolt holes 25 whereby the photocell means i8 and i9 adjacent the outer cylinder H. The housing member M has a downwardly extending hollow, preferably tubular,

' pivot member 43 in which a light source is may plastics, or any material that will be unafiected by the fluid being analyzed. The smaller or inner groove or channel 28 is coaxial with the axial bore 24 while the larger surrounding groove 2? is eccentric with regard to groove 28 so that preferably, the distance between rthegrooves at their most widely separated points issevcral times the distance at diametrically opposite points. when the transparent cylinders H and i2 are mounted in the eccentric grooves 2'? and 28, a fluid container or cell 3! is formed between the cylinders which possesses sections of varying width or thickness.

If desired, the top :of the fluid or absorption container or cell .34 may :be:closed by a cell cover 13 which may be secured to the upper flange member 22 of the base member ID by any suitable means, as by bolts 33.- The cell cover 13 also may have eccentric grooves 32 and 34 cut therein in which the :upperiedges of the cylinders I I and I2 may be positionedand sealed by gaskets 35 and 3B of a suitable fluid-resistant material. The fluid cell 3| is equipped with suitably disposed 'fluidinlet and outlet means, 31 and 38 respectively. Inthis embodiment, both the fluid inlet 3'! and outlet 38 pass through the bottom of the fluid cell 31, or the top flange member 22 of the base unit it). The fluid outlet 38 is equipped with a standpipe-39 located within the cell 3! to insure circulation of the fluid sample therein. The fluid inlet 3-"! may have a short nozzle 43 attached whereby the influent fluid is directed toward the smallest section or width of the fluid cell 1-H andnear the. bottom thereof.

In the event that thexsample being tested is a fluid, there isa tendency for-the influent liquor to circulate in the widest or less restricted portion oi the fluid cell 31,, causing said fluid to stagnate in the narrower portions of said cell 3!, thus allowing a non-representative sample to be analyzed while at the same time causing diffcrential contamination or beclouding action on the inner surfaces of the transparent cylinders M and I2. Differential contamination of an instrument of this type -is-one of theprimary causes of error, especially in instruments used with continuously flowing liquids. In the present apparatus by circulating:theliquidsample through the narrower portionsof the cell 31 as it enters, a representative sample is availableior analysis at all times-while the-.influent liquid exerts a washing action: on the inner walls of the cell 3i. While the outer cylinder ll may be eccentrically positioned about and at any distance from the inner cylinder 12, the-distance between the two cylinders where they are closest to each other is preferably large enough to allow a sufficient flow of liquid therethrough to-flush the walls of said cylinders. Anyirnpuritiesthat settle out of the fluid sample being analyzed may be removed through a drain port M- (Figure 2) located 'between the cylinders l-l and-l2 in the upper flange member 22 of thebas member Hi. This drain port ll is normally closedby any suitable means as by a plug 42, valve, orthe like.

Mounted rotatably and in coaxial relationship with the axial bore 24 of the pedestal H] is a housing member 14, 'rotatably mounting the Thus be fixedly mounted in any suitable manner. The lower end of the pivot member 43 may be mounted rotatably in the axial bore 245 of the pedestal in in any suitable manner. One method of mounting said pivot member 43 is shown in Figure l wherein an outwardly extendin flange means 4% is fixedly secured to or integrally formed on the outer wall of the pivot member 43, said pivot member being, rotatable on a bearing as which is fixedly'mounted on a shoulder 56 with- V in the axial bore 24m the pedestal it. The lower end of said pivot member i3 may rotate in a second bearing 41.

The housing member 14 may be of any desired shape. In the embodiment illustrated in Figure 1, the housing member .[4 is shown as a drumlike structure surroundingith cylinders H and i2, and having an open lower end which is substantially closed by the upper flange 22 of the pedestal it when the housing is mounted in its operating position. The drum-shaped housing member I4 is integrally formed with or fixedly secured to the upper end of th housing pivot member 43 in any suitable manner as by welding, screw-threads, etc. The top of the housing pivot member 53 is preferably open to allow heat from the lamp 15 to be dissipated more readily. It may be desirable however to cover the open upper end of said pivot member by a perforated dust cap or ventilator 48' in order to keep dust off the light source The drum-shaped housing M, which is preferably blackened inside to cut down reflected: light and which covers the entire instrument, .ofiers substantial protection tothe glass cylinders H and 42.

The two light sensitive or photocell means 18 and i9 which maybe photocells of the self-generating or variable resistance type or phototubes, may be fixedly secured in any suitable manner to the outer walls of the housing i i, said photocell means preferably being located substantially opposite each other. The electrical conduits 45 and 50 leading :to the photocells 8- and i9 and the electrical conduit 5| to the light source it should be of sumcient'length-so that the housing It and attached photocells and lamp may be freely rotated. A-pair of collimating slits 52 and 53 are cut or for-medin: the walls of the tubular pivot member &3, saidzslitspreferably being substantially opposite each other and preferably opposite the brightest portion of the light source i5. Disposed radially from slits 52 and 53 is a second pair of slitsE-ll and'fiii in the housing Hi. If desired, lens systems maybe used for collimating the light from lamp into suitable beams that would be .defined'by slits 52 and '53. When the photocells l8 and i9fare'secured to the housing it they are positioned with regard to slits 54 and 55 so that the *lightbe'ams emanating from the light source 15 fall on the photocells. The size of theslits 52,153, 54 and 55 is therefore generally determined by the effective area of the photocells Wendie. The area of the slits 5 3 and 55 may be varied hy any suit-able type of adjustable diaphragm means as by movable screens or slides 5'6 and El which may be controlled by adjustment screws 58 and 59. Dust or other contaminating materials may be substantially excluded from the photocell surfaces by covering them withshieldsor dust caps BE) and- If desired, removable light filters l3 and 19 may be inserted in front of the photocells l8 and I9.

Since a considerable amount of heat may be generated by the light source I5, the pedestal It may be equipped with an air inlet I8 and the tubular pivot member 43 may have air circulation holes 19 whereby air may be blown through the tubular pivot member 43 to cool it. If a sample of a volatile and inflammable liquid is to be analyzed the blowing of air through the instrument in the above-described manner will also remove any explosive vapors from the vicinity of the light source I5, said vapors being origin-- ally due to a possible leaking gasket at the top or bottom of the cylinders II and I2. While the instrument is being used a retainin ring or plate 64 may be secured to the bottom of the housing I4 50 as to extend under the upper flange 22 of the pedestal It! thus preventin the housing from being accidentally lifted.

When readings are being taken with the abovedescribed instrument the movable housing member I4 is positioned fixedly with regard to the base member ID by any suitable anchoring means. One such anchoring means is shown in Figure 2 comprising a mounting 65 fixedly secured to the lower edge of said housing I4 having a springloaded plunger 66 extendin therethrough to engage spaced positioning notches, slots or terminals 6'! and 68 which may be cut or formed in, or near, the periphery of the upper flange member 22 of the base member ID, preferably about 90 apart on said periphery. The location of one notch El is selected by the setting of the cooperating plunger 66 when the movable housing I4 is positioned with respect to the eccentric cylinders II and I2 so that equal thickness of fluid between said cylinders II and I2 will be interposed between the light source I5 and the photocells I8 and I9.

The light source I5 may be mounted in any suitable manner, as in a socket 69, preferably in a fixed position relative to the pivotal member 43 and within the inner transparent cylinder I2 whereby the light source is rotated with the housing member 14 thus maintainin an optical relation between the light source I5 and the photocells I8 and I9 such that the rotation has substantially no optical effect other than the interposition of different cell-depths or thicknesses of fluid. A light source I5 emitting white light is normally used. The spectral characteristics of this light may be varied if desired by inserting suitable filters. The use of filters or other types of light, e. g. monochromatic light, may be useful in determining the hue of the fluid being analyzed. Determination of hue may be also facilitated by the use of diiferent lam characteristics, i. e. by changing the lamp filament temperatures so that the transmission measurements can be applied to broader color characteristic determinations.

Line voltage variations that normally influence the brightness of the light source may be compensated for by use of a ratio-measuring circuit such, for example, as that shown in Figure 3. In this form of circuit, 8|] represents a tapped resistor or a slidewire, while 8| and 82 are resistors which may be of the fixed or the variable type. By suitable choice of resistance values, the instrument may be made to indicate, by the position of the movable contact 85 along the slidewire 86, any desired range of color density or transmissivity. The measuring photoelectric cell I8 is connected across the combined resistors 80,-

8| and 82, and a null-indicating device 86 is con nected across these same resistors. Reference photoelectric cell I9 is connected across resistor 8! and the adjacent portion of slidewire 80. The two photoelectric cells have opposite polarities connected to resistor 8i, and this point may be grounded to the instrument frame or housing as at 83. Switching means 84 are provided for short-circuiting resistor 82 from the circuit when the colorimeter is being checked or zeroed as described hereinbelow.

The operation of this circuit is as follows. Briefly it may be said that if movable contact 85 is brought to such a point that the resistance across photoelectric cell I9 (R) bears the same relation to the total resistance as the photoelectric current delivered by photoelectric cell I8 (M) bears to the photoelectric current delivered by photocell I9 (R), then the null indicator 86 will show no deflection; while otherwise the deflection of the null indicator will show which way to move contact 85 to obtain this balance. Furthermore, this balance may be obtained automatically and substantially continuously by linking null indicator 86 with a mechanical system for moving contact 85, as is done in self-balancing potentiometers in a manner well known in the art. Since the aforementioned resistance ratio may be simply related to the position of a pointer 85 sliding on resistance 80, or a pen on a chart of a recording self-balancing potentiometer; while the aforesaid ratio of photoelectric currents is equal to the ratio of illumination of the two photoelectric cells, it follows that a direct record or indication of relative illuminations will be given by this arrangement. It is understood that other arrangements may be used alternatively, in a similar manner, although the arrangement described is a preferred one.

From the above description of the apparatus and electrical circuit it is evident that by utilizing eccentrically mounted glass cylinders II and I2, the radial thickness of a fluid between said cylinders will vary with rotation of the housing about the axis of the instrument or about the smaller cylinder I2. Thus by rotation of the housing I4 which carries the lamp I5, slits 52, 53, 54 and 55 and photocells I8 and IS, the two beams of light from the lamp I5 which pass through the oppositely located collimating slits may be made to traverse any selected thickness of fluid between the eccentric cylinders I I and I2 providing the fluid level is above the light beams. For ease of description it will be assumed that the fluid being analyzed is a petroleum oil. When the housing I4 is positioned with relation to the eccentric cylinders II and I2 as shown in Figure 2 the light beam to one of the photocells I 8 will be traversing the maximum oil thickness or layer (say 35 mm.) while the light beam to the other photocell I9 traverses the minimum oil layer (say 5 mm.). This position of the photocells may be termed the measuring position. For a quick setting of the instrument to this position at any time it is only necessary to rotate the housing I4 until the spring-loaded plunger 66 slips into positioning notch 68 as shown in Figure 2. With the housing I4 located in this measuring position the two light beams to photocells I8 and I9 will traverse paths involving a difference in oil thickness of 35-5 or 30 mm., so that the effect of the light striking the measuring photocell I8 will differ from that striking the reference photocell I9 by an amount which depends on the absorption of light by theaeomee oil, the optics of the system; the incident light distribution and the photocell sensitivities. When this group of factors is kept constant asit is when the lamp l5, slits 52, 53, 54 and 55 and photocells l8 and it are rigidly mounted, the ratio or the light falling on'the photocells is an indication of the absorption of the oil, Thus by connecting the two photocells l8 and 19 in a ratio-measuring circuit as shown in Figure 3, the readings obtained therefrom may be correlated with the color density measured visually by any standard colorimeter.

Since one of the advantages of the instrument of the present invention isits adaptability for either continuous operation or for individual runs or samples, provision is made for minimizing and detecting the incidence of errors such as might be caused by: (1) line voltage variations changing the total light from lamp l5, (2) differential deterioration of the photocell sensitivities, (3)

differential contamination, by dust, etc., of the lamp, slits and photocell surfaces and (4) differential contamination of the glass surfaces by the oil in the absorption cell 3i. Taken in the above order, these sources of error may be minimized and substantially eliminated by (1) using a ratio circuit, as shown in Figure 3, and matched photocells, (2 providing shutter means for varying the area of each photocell exposed to the light beam, (3) using a symmetrical design of the instrument and providing suitable dust shields, and (4) flowing the fluid sample over all the surfaces of the fluid cell 3!.

An especially important feature of the present invention is its ability to detect the incidence of errors due to' the above-mentioned causes. In order to accomplish this purpose, it is important that the fluid or absorption cell 3! be so constructed that in one position of the instrument, which will be called its zero position, the fluid thicknesses in the paths of the two light beams are equal. With the two oilthicknesses equal, the color density or transmissivity of the oil does not affect the reading obtained and it is therefore possible to check the instrument to ascertain whether conditions have remained constant or if other errors have been introduced.

In operation, the colorimeter of the present invention. is suitably mounted in an upright position with its inlet 31 and outlet means 38 conbeing made or shut off when the instrument is not in use or is being cleaned. When making continuous readings or recording with the instrument, both inlet and outlet valves 12 and 73 are opened allowing the fluid to flow through the fluid or absorption cell 3!. The instrument is then checked or zeroed to detect cumulative errors due to unequal aging of the photocells i8 and 19 or to the accumulation of foreign matter in unequal proportions on the walls of the absorption cell 3|, in the slits or on the photocells. The housing id is moved into zeroing. position by grasping handle 74 (Figure 2) to withdraw plunger tt from notch 88 and rotating said housing i4 until the plunger is opposite the zeropositioning notch Bl at which. time the plunger is released, allowing it to enter said notch 67. While the housing i4 is being rotated to its zero position, the switch 34 (Figure 3) is closed, which short-circuits resistor '82 from the circuit to place the zero reading of the potentiometer 60 on its scale. The closing of switch 84 may be accomplished automatically by having the switch mounted in any suitable manner on the rotatable housing 14 as shown in Figure 2. When the housing is rotated to the zeroing position, the switch 34 is actuated by a leverarm 81 which may be fixedly secured to the pedestal 19. With theinstrument in its zeroing position, the thicknesses of the fluid in the paths of the two light beams and therefore, when the instrument is in proper adjustment, the outputs of both photocells l8 and is are equal so that no voltage will be noted on the indicating device and the sliding contact 85 will seek the zero reading of the potentiometer Bil when a self-balancing potentiometer is used. If a reading other than zero is indicated, adjustments may be made to screen 56 or 5? to restore the instrument to zero balance. To obtain a color density or spectral transmission reading of the fluid being analyzed, the housing is rotated in the manner previously described until the positioning plunger is located in the measuring notch 68, at which time switch 84 is opened putting resistor 82 back in the circuit. With the instrument now set in this measuring position, the thicknesses of the fluid intercepting the two light beams are substantially different, causing a diiierential output of the photocells iii and 59. This voltage difference shown as appearing on the indicating device 86, if applied to the self-balancing potentiometer, causes the sliding contact of the potentiometer fill to seek a new balance point. The reading on ,he instrument obtained by this new balance point is an indication of the amount of light being transmitted through the unknown fluid being analyzed. A sample of the fluid in the absorption chamber 3! may be drained off and tested in a standard colorimeter to obtain a reading corresponding to that of the potentiometer 80. By testing a number of differently colored fluid samples with the present instrument and with a standard colorimeter, a calibration curve may be obtained by which the potentiometer readings of the instrument of the present invention may be conveniently translated into standard readings.

The design of the present apparatus permits to check for the cause of any error which may appear when readings are taken. For example, if readings were taken in the original zero and measuring position at the beginning of a set of tests, and a subsequent zero reading was different from that originally taken, an error is indicated which may be due to either of the two following sets of conditions. First, there may be unequal deterioration in the sensitivity of the photocells or an accumulation of dust on the slits 52 53, 54 and 55, lamp i5 or photocells l8 and I9; 01, second, there may be unequal contamination of the glass walls of the absorption cell 3|. The absorption cell 3! may be then drained and readings taken in both the zero and measuring positions of the instrument again. If both readings disagree with the original values by approximately the same amount, the error is due to unequal deterioration of the photocells or duston the slits, lamp or photocells. Compensation for this error may be made by resetting one of the adjustment screws 58 or 59 thus opening or closing slide or shutter 55 or 51 until the new zero reading equals the original zero reading. If, however, after making the above comparison between the original values obtained and the new values, it is found that the differences or water-white fluid, e. g. kerosene.

'instrument is in its measuring position.

unequal contamination of the glass walls of the absorption cell. This may be remedied by cleaning the cell in any suitable manner, as by flush- I ing it with a solvent, cleaning solution or the like.

' Although the above-described embodiment of the present invention may be used to determine the amount of light transmitted by a fluid of any color and over any range of said color, certain modifications may be made to the instrument when it is used to analyze a substantially clear It will be noted that since the transparent cylinders II and I2 are eccentrically positioned, the fluid in the absorption cell 3I that is cut by the diverging light beams (represented by dotted lines in Figures 4 through 9) constitutes a lens when the This is illustrated diagrammatically in Figure 4 wherein the shaded or cross-hatched portions IIII and I 02 represent the lenses of fluid. These lenses of fluid tend to change the intensity of the light passing through the fluid so as to give incorrect readings on various colorless fluids. For example, if a reading is taken with the instrument in its measuring position and with only air in the absorption cell 3|, and then a second reading is taken after filling the cell with a nearly colorless liquid such as kerosene, the reading in the second case might indicate that the transparency of the kerosene was greater than that of an absolutely transparent medium because of the lens effect of the segments of fluid. Effects of refraction of this type may be reduced by use of slits or lenses that permit only parallel beams I I3! and I32 of light to pass through the liquid,

as shown in Figure 7. The lens eiiect may be entuely eliminated if the absorption cell has parallel walls. As diagrammatically shown in Figure 8 the absorption cell MI may comprise two transparent cylinders I42 and I43 having diametrically opposing surfaces flattened slightly at Md, M5, M6 and I41 so that the light beams I 48 and I49 pass through parallel walls which do not refraot the light. Another embodiment is shown in Figure 9 wherein the parallel walls of the absorption cell I5I comprise transparent rectangular members I52 and I53 through which light beams I54 and I55 may pass without being distorted or refracted, the member I52 being linearly movable as described hereinbelow with regard to Figure 10.

Another slight source of error that may be introduced into readings, taken with the instrument in its zero position, is due to the use of eccentrically positioned cylinders. As shown in Figure 5 the segments of fluid between the eccentric cylinders III and H2 that are cut by the light beams I I3 and I I4 are in the form of prisms I I5 and I I6 which slightly distort the instrument reading in its zero reading position. The distortion errors may be compensated for by positioning the photocells I8 and I6 on the housing Id so that the angle between them is slightly less than 180 degrees, as shown in exaggerated form in Figure 6. Use of an absorption cell I5I constructed as shown in Figure 9 and previously described will entirely eliminate this source of error.

One of the advantages of the present colorimeter is that it may be readily zeroed or checked for source of error while the sample fluid intercepts the light beams, whereas conventional colorimeters are usually checked with a reference liquid, such as water, in the absorption or sample cell. It has been found advantageous to check the instrument with the sample in the absorption cell as this allows both the checking and measuring operations to be made under substantially the same spectral conditions. Thus the photocells are not exposed to extreme operating conditions as only an average amount of light falls on the photocells when they are being checked.

Although the embodiments of the colorimeter that have been described have all been limited to a housing adapted for rotational motion about the absorption cell or test chamber 3I, it is evident that a similar colorimeter could be adapted to be mounted for longitudinal motion adjacent a transparent portion of a fluid pipe line. An important feature of the colorimeter, when used with continuously flowing fluids, is that fluid depths of equal and unequal thicknesses be interposed between the light source and the photocells when the instrument is in its checking and measuring positions, respectively. This arrangement of the instrument with regard to the absorption cell also may be achieved by an arrangement of the light and photocells, as shown in Figure 10. In this embodiment the absorption cell I60 comprises a section of transparent conduit in a bypass I6I of a fluid flow line I62, said conduit I60 being formed into portions having two different thicknesses. Valves I63 and I64 in the by-pass and I65 and I66 in the flow line may be set to control the desired flow therethrough. Movably mounted for longitudinal movement along said absorption cell I60 is the colorimeter housing I61. The housing may be mounted in any suitable manner as, for example, on wheels I68 which move along a track I69 suspended from the bypass IBI by rods I10 and Ill. Contained within the housing I61 are the elements of the first embodiment namely, a light source I12, a light shield I15 having collimating slits I13 and I14 therein,

and photocells I16 and I11, all of said elements being mounted rigidly to said housing in any suitable manner. Thus, it will be seen that when the colorimeter is connected to a power source and the housing I61 is in its measuring position A, as shown in Figure 10, the beams of light from the light source I12 pass through portions of the absorption cell having different thicknesses and therefore containing different depths of the fluid to be measured which will in turn result in a measurable difference in current output between the two photocells I 16 and I11. in output may be measured, indicated or recorded by use of an electrical circuit as shown in Figure 3 and previously described. Now, when the colorimeter housing I61 is moved to its checking or zeroing position B, equal thicknesses or depths of fluid in the conduit are interposed between the light source I12 and the photocells I16 and I11 so that the illumination of the photocells is equal, thus resulting in an equal output therefrom, if they are in correct adjustment.

In practice, the colorimeter of the present invention may be installed in a fluid flow line H, as shown in Figure 11, to control the color of the flowing fluid and/or to record changes in the spectral transmission of the fluid. This may be accomplished by connecting the photocells I8 and I9 with a self-balancing potentiometer or recorder-controller I6, such for example as manufactured by the Brown Instrument Company (Bulletin No. 15-4, 1942), the Tagliabue Manufacturing Company (Catalog No. 1101E, 1939), the Leeds-Northrup Company (Catalog No.

This difference 33-161, 1940), etc. ,The self-balancing potentiometer and controller l6, which is supplied with an operating current from any desired source through leads H, rebalances itself, .in .a wellknown manner, after any condition of unbalance caused by variations of the currents supplied by the photocells l8 and [9. .In rebalancing itself, the recording and controlling potentiometer I6 delivers an energizing current, which serves to produce the desired record and which is also applied through leads 20, to control the degree of closure of an automatic valve 21 which in turn maycontrol the flow of a colored fluid from fluid conduit 90 into the main fluid stream H. For example, if the color'of the fluid in the flow line H became less transmissive it would change the output of the photocells l8 and 19, thus causing a change in the recorder-controller it which in. turn would reset the valveli so that the amount of colored fluid entering the main flow line H would be decreased.

It is understood that all examples were given hereinabove {merely by Way of illustration and that the scope of the present invention and its applicationfor purposes of industrial control are in no way limited thereby, being defined only in the claims hereinbelow.

We claim as our invention:

1. An apparatus for measuring the optical transmissivity of a fluid, comprising a housing, a

source of light rays positioned centrally of said housing, first and second light-sensitive means carried by said housing on diametrically opposite sides from said lightsource, transparent annular container means surrounding said light source Within said housing,said annular container means having an inner wall concentric with said light source and an outer wall eccentric therewith, means for introducing a light-transmissive liquid into said transparent container means, and means i for rotating said housing andsaid light-sensitive means with regard to said annular container about an axis transverse to a straight line passing through said light-source and said two ligh sensitive means so as to change the ratio of the lengths of the paths of the rays from said source to said first and to said second light-sensitive means through the liquid in said container.

2. The device of claim 1, comprising latch means for clamping said housing with regard to said annular container in a first position wherein said ratio of path lengths has a value of one and in a second position wherein said ratio has a maximum value.

3. An apparatus for measuring the optical transmissivity of a fluid, comprising a frame member, a source of light rays and first and sectransmissivity of a fluid, comprising a frame member, a source of light rays and first and second light-sensitive means supported by said frame member at fixed distances vfrom each other,

transparent container means disposed in the paths of travel from said source to each of said light-sensitive means, means for introducing "a light-transmissive fluid into said transparent container means, and-means .for displacing said frame member and said container with regard to each insuch a manner as .to change the rela- .tive lengths of the paths of the rays through said light-transmissive fluid from said source to said first and to said second light-sensitive means whereby the amount of light received by one of .said light-sensitive means from said light source may be compared with that received by the other light-sensitive means .for a relative position of said frame member and said container where the ratio of the path traversed by the rays through said light-transmissive fluid between said light source and the first light-sensitive means to the path traversed thereby .throughsaid light-transmissive fluid between .said light source and the other light-sensitive means has a maximum value and for a relative position of said frame and said container where said ratio has a value of one.

GEORGE-C. ELTENTON. MARVIN B. FALLGA'I'IER.

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